Breast cancer is one of the largest classes of malignant disease in women. However, breast cancer presents inherent difficulties in regard to the ease with which it is detected and diagnosed. This is in contrast to detection of some other common cancers, including skin and cervical cancers, the latter of which is based on cytomorphologic screening techniques.
Early detection of breast cancer represents a compelling goal in oncology. Although techniques such as computerized tomography, mammography, and magnetic resonance imaging have greatly improved tumor surveillance over the past decade, there still remains a need for serologic and other blood-based assays.
Serologic assays are easily performed, inexpensive, and analytically-sensitive and can be serially run over time with relative ease. The essence of breast cancer screening, using tumor marker detection, is to efficiently identify a group of higher-risk individuals from within a large population. Thereafter, confirmatory testing is implemented to establish a diagnosis of malignancy.
There are several classifications of tumor markers possible, based upon the structure or biological function of the marker. Tumor marker classifications include tissue specific antigens (e.g., PSA, NSE, PAP, calcitonin, HCG), major histocompatibility complex ("MHC") antigens, viral antigens (e.g., HTLV-I gag protein), oncogene products (e.g., c-HER-2/Neu), oncofetal markers (e.g., CEA, AFP), hormones (e.g., thyroid hormones), enzymes (e.g., telomerase, galactosyltransferase), and altered glycoproteins/glycolipids (e.g., polymorphic epithelial mucins). It should be noted that these classification schemes are imprecise and contain redundancies. For example, calcitonin is an important serological marker for medullary carcinoma of the thyroid and may be classified not only as a hormone but also as a tissue specific protein of the thyroid. Likewise, PSA, HCG, thyroid hormones, PAP, and NSE are tissue specific proteins and also exhibit enzymatic or hormonal activities. Generally, tumor markers providing high clinical utility reside in the broadly defined tissue specific class. This class of tumor markers contains enzymes, isoenzymes, hormones, growth factors, and other molecules with biologic activity.
The importance of a tumor marker's being tissue specific is illustrated by one of the best known tumor antigens, carcinoembryonic antigen ("CEA"). When first discovered, CEA was thought to be specific to cancers of the digestive system. However, CEA has since been detected in normal adults as well as in patients with benign liver disease, such as alcoholic hepatitis or biliary obstruction. Because of the overall lack of specificity and sensitivity, there being no threshold difference in CEA levels that serves to separate benign from malignant conditions, CEA cannot be used in a general diagnostic test. Instead, it is principally used to monitor a patient's response to treatment.
To be useful in serologic assays, a tumor marker should be one that is released into the bloodstream as a circulating marker. Circulating antigens are now known to exist in breast cancer. Breast tissue markers, such as casein (Franchimont et al., Cancer, 39:2806-2812 (1977)) and .alpha.-lactalbumin (Kleinberg et al., Science, 190:276-278 (1975)) and purported cancer markers, such as glycosyl transferases (Ip et al., Cancer Res., 38:723-728 (1978) and Dao et al., J. Natl. Cancer Inst., 65:529-534 (1980)), glycolipids (Kloppel et al., Proc. Natl. Acad. Sci. USA, 74:3011-3013 (1977)), and phospholipids (Skipski et al., Proc. Soc. Exp. Biol. Med., 136:1261-1264 (1971)) have all been used in various diagnostic techniques for breast cancer but have not gained widespread acceptance as breast cancer markers. More recently, circulating human mammary epithelial antigens have been proposed as specific markers for breast cancer (Ceriani et al., Proc. Natl. Acad. Sci. USA, 79:5420-5424 (1982)). Burchell et al., Int. J. Cancer, 34:763-768 (1984) describes monoclonal antibodies which detect high molecular weight mucin-like antigens elevated in patient serum. Hayes, J. Clin. Invest., 75:1671-1678 (1985) also describes a monoclonal antibody that recognizes a high molecular weight mammary epithelial antigen present in elevated amounts in the plasma of breast cancer patients. See also Papsidero et al., Cancer Res., 44:4653-4657 (1984) and Taylor-Papadimitriou et al., Int. J. Cancer., 28:17-28 (1981). Other breast tissue specific proteins or markers include alpha, beta, and kappa caseins, alpha-lactalbumin, lactoferrin, and selected epithelial membrane antigens. These are described in Cohen et al., Cancer, 60:1294-1298 (1987); Bartkova, Eur. J. Cancer Clin. Oncol., 23:1557-1563 (1987); Weir et al., Cancer Detect. Prev., 4:193-204 (1981); de Almeida et al., Breast Cancer Res. Treat., 21:201-210 (1992); Skilton et al., Tumor Biol., 11:20-38 (1990); Earl et al., Cancer Res., 49:6070-6076 (1989); Barry et al., Amer. J. Clin. Path., 82:582-585 (1984); and Watson et al., Cancer Res., 56:860-865 (1996). None of these previously described antigens has been used as a basis for a widely accepted breast cancer clinical assay.
There have also been several attempts to develop improved methods of breast cancer detection and diagnosis based on oncogene mutations, gene amplification, and loss of heterozygosity in invasive breast cancer. These methods have not gained wide acceptance.
Despite the use of mammography and the development of some breast tissue specific markers, there still remains a need for simple and rapid methods for detecting breast cancer. The present invention is directed to meeting this need.